Thermogravimetric-mass spectrometric analysis of the reactions between oxide (ZnO, Fe2O3 or ZnFe2O4) and polyvinyl chloride under inert atmosphere

The mechanisms of reactions are investigated between polyvinyl chloride and oxides such as ZnO, Fe2O3 and ZnFe2O4 under inert gas atmosphere at high temperature with combined thermogravimetry-mass spectrometry (TG-MS) technique. From the experiments under a constant heating rats of 40 K/min, the following results are obtained. In the case of mixture pellet of ZnO and PVC, the chlorination of Zn in ZnO to ZnCl2 by Cl in PVC starts at a relatively low temperature about 473 K without the formation of HCl. The chlorination is followed by the de-hydrochlorination of residual un-reacted PVC, also by the further degradation to lower order hydrocarbons, and finally by the evaporation of ZnCl2 at higher temperature. On the other hand, in the case of ZnO-PVC double layer pellet in which ZnO layer is compacted at the top of PVC layer, PVC decomposition accompanying HCl formation starts at about 523 K, which is similar to the thermal decomposition of pure PVC in the absence of the oxide. The chlorination of Zn is not favored in this case of double layer sample. In the case of Fe2O3-PVC mixture, the de-hydrochlorination takes place at the temperature range of 513 to 673 K, similarly with the case of the pure PVC decomposition. With increasing temperature, the degradation of de-hydrochlorinated PVC residue to lower hydrocarbons and the stepwise reduction from Fe2O3 to metallic Fe takes. place after the de-hydrochlorination. The reaction scheme of ZnFe2O4-PVC system shows intermediate character between ZnO-PVC system and Fe2O3-PVC system. The kinetic mechanisms of the reaction between the oxides and PVC are examined on the basis of the experimental results.